The current time as returned by the time function followed by a period. The value is dislayed in decimal and is the number of seconds since midnight on 1 Jan 1970. In the example above, 1185616355 refers to Sat, 28 Jul 2007 09:52:35 GMT.

The process id number in decimal followed by a period

The third value starts at zero but may increase as more messages are sent. It is also followed by a period

The word camel followed by an '@'

If the canonical hostname can found, it is used. Otherwise the hostname

The Message id format comes from the function camel_header_msgid_generate in evolution-data-server/camel/camel-mime-utils.c.